1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, more particularly to a novel electrophotographic photosensitive member containing a bisazo compound.
2. Description of the Prior Art
In the electrophotographic photosensitive members of the prior art, those having inorganic photoconductive materials such as selenium, zinc oxide and cadmium oxide as the main component have widely been used. However, these were not necessarily sufficiently satisfactory in sensitivity, heat resistance or printing resistance.
On the other hand, in recent years, electrophotographic photosensitive members comprising photosensitive layers containing organic photoconductive compounds as the main component are attracting attention. These have a number of advantages of relatively easy preparation, low production cost, applicability for any desired shape such as cylindrical drum or sheet, easy handling, excellent heat resistance and others. However, for example, in an electrophotographic photosensitive member having a photosensitive layer composed mainly of a charge transfer complex formed from poly-N-vinylcarbazole and a Lewis acids such as 2,4,7-trinito-9-fluorenone or the like, which has already practically been used, the results obtained are not necessarily satisfactory with respect to sensitivity and printing resistance.
Meanwhile, since the invention of a function separation type electrophotographic photosensitive member of the layered type or the dispersed type, in which the carrier generating function and the carrier transporting function from the aspect of photoconductive function are divided to be possessed by separate materials, various advantages have been brought about. Such a function separation type electrophotographic photosensitive member has the advantages of attaining relatively easily high performances in electrophotographic characteristics such as charging characteristic, sensitivity, residual potential, etc. as well as in printing resistance and also of easy preparation of an electrophotographic photosensitive member having desired characteristics.
As the carrier generating material undertaking primarily the function of carrier generation in an electrophotographic photosensitive member having such advantages, various inorganic and organic materials have been proposed to be used. As an inorganic material, a carrier generating layer fromed from amorphous selenium is well known, but this has the drawback of being crystallized under high temperature conditions to be deteriorated in performance. On the other hand, as an organic material, materials selected from among photoconductive organic dyes or pigments have been variously proposed to be used, particularly for carriergenerating materials, as exemplified by azo compounds disclosed in U.S. Pat. No. 3,898,084, Japanese Provisional Patent Publication Nos. 95033/1978, 22834/1979, 79632/1979 and 116040/1981. However, these azo compounds are not necessarily satisfactory in such characteristics as sensitivity, residual potential or stability when repeatedly used. Also, the carrier transporting material must be selected from a limited range of materials, and, under the present situation, there is obtained no electrophotographic photosensitive member which can satisfy sufficiently the broad scope of requirements in electrophotographic process.
Further, in recent years, as the light source for a photosensitive member, a gas laser such as Ar laser, He-Ne laser and the like or a semiconductor laser is coming to be used. These lasers are capable of on/off in time series, can perform high resolving recording at high speed and also enable a diversity of recording modes. Therefore, they are expected to be very promising, particularly for copying machines having image treating functions, including intelligent copier, or printers for output of computers. Among them, a semiconductor laser is attracting attention, because, by virtue of its characteristics, it can dispense with an electrical signal/optical signal converting element such as an acousatic optical modulator, and also enables miniturization and weight reducton of the device. However, this semiconductor laser is lower in output as compared with a gas laser, and its oscillation wavelength is longer (about 780 nm or longer), and therefore it is impossible to use a semiconductor laser as the light source for a photosensitive member of the prior art, of which spectral sensitivity is shifted too much toward the shorter wavelength side.